01-07-2010, 01:55 PM
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1. Introduction:
1.1 RECOGNITION OF OPTICAL CAMOUFLAGE:
In 2003, three professors at University of Tokyo †Susumu Tachi, Masahiko Inami and Naoki Kawakami †created a prototypical camouflage system in which a video camera takes a shot of the background and displays it on a cloth using an external projector. The same year Time magazine named it the coolest invention of 2003. With flexible electronics such as a flexible liquid crystal display that would permit display of the background image by the material itself, this form of optical camouflage may closely resemble its fictional counterparts.
Various methods have been proposed to integrate the visual space. In the field of Mixed Reality, one of the most popular topics is about displaying a virtual object into real world.However making objects virtually transparent, like in H.G. Wellsâ„¢ Invisible Man can also be seen as dream of human being. In this paper, we describe what could be called a camouflage technique named Optical Camouflage.
1.2 WHERE HAVE U SEEN OPTICAL CAMOUFLAGE:
¢ Ghost in the Shell.
¢ 2000 video game Deus Ex.
¢ 2002 James Bond movie Die Another Day
¢ Metal Gear Solid and Halo video game series.
¢ The video game Phantom Crash.
¢ The Predator movie.
Invisible - A Reality or fiction
Is becoming invisible confined only to the world or fiction or can it be achieved in reality The answer is YES! Thanks to the technology -Optical Camouflage with retro-reflective projection. Today invisibility is no more a fictional concept.
What makes objects visible
Before going into the concept of invisibility, let us first see what makes the objects around us visible
¢ Why are we able to see objects around us
Scattering of light
¢ A look at the law of reflection.
The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection
¢ What do we mean by Retro-reflection
Retroreflection is a special kind of reflection where the light is reflected.
Finally lets come to OPTICAL CAMOUFLAGE.
2. WHAT IS OPTICAL CAMOUFLAGE
¢ Optical camouflage is a hypothetical type of active camouflage currently only in a very primitive stage of development. The idea is relatively straightforward: to create the illusion of invisibility by covering an object with something that projects the scene directly behind that object .
¢ Optical camouflage is a kind of active camouflage which completely envelopes the wearer. It displays an image of the scene on the side opposite the viewer on it, so that the viewer can "see through" the wearer, rendering the wearer invisible.
¢ Although optical is a term that technically refers to all forms of light, most proposed forms of optical camouflage would only provide invisibility in the visible portion of the spectrum. Prototype examples and proposed designs of optical camouflage devices range back to the late eighties at least, and the concept began to appear in fiction in the late nineties.
Optical camouflage is a kind of active camouflage. This idea is very simple. If you projectbackground image onto the masked object, you can observe the masked object just as if it were virtually transparent. Although optical is a term that technically refers to all forms of light, most proposed forms of optical camouflage would only provide invisibility in the visible portion of the spectrum.
The most intriguing prototype uses an external camera placed behind the cloaked object to record a scene, which it then transmits to a computer for image processing. The computer feeds the image into an external projector which projects the image onto a person wearing a special retroreflective coat. This can lead to different results depending on the quality of the camera, the projector, and the coat, but by the late nineties, convincing illusions were created.The downside is the large amount of external hardware required, along with the fact that the illusion is only convincing when viewed from a certain angle.
Creating complete optical camouflage across the visible light spectrum would require a coating or suit covered in tiny cameras and projectors, programmed to gather visual data from a multitude of different angles and project the gathered images outwards in an equally large number of different directions to give the illusion of invisibility from all angles. For a surface subject to bending like a flexible suit, a massive amount of computing power and embedded sensors would be necessary to continuously project the correct images in all directions. This would almost certainly require sophisticated nanotechnology, as our computers, projectors, and cameras are not yet miniaturized enough to meet these conditions.
Although the suit described above would provide a convincing illusion to the naked eye of a human observer, more sophisticated machinery would be necessary to create perfect illusions in other electromagnetic bands, such as the infrared band. Sophisticated target-tracking software could ensure that the majority of computing power is focused on projecting false images in those directions where observers are most likely to be present, creating the most realistic illusionpossible.
3.HOW DOES IT WORK
Creating complete optical camouflage across the visible light spectrum would require a coating or suit covered in tiny cameras and projectors, programmed to gather visual data from a multitude of different angles and project the gathered images outwards in an equally large number of different directions to give the illusion of invisibility from all angles. For a surface subject to bending like a flexible suit, a massive amount of computing power and embedded sensors would be necessary to continuously project the correct images in all directions. This would almost certainly require sophisticated nanotechnology, as our computers, projectors, and cameras are not yet miniaturized enough to meet these conditions.
First, putting the video camera behind the person in the cloak, and capturing his background. Then, projecting the captured image onto the cloak from the projector. So, if you see from the peephole, you will see as if the cloak is transparent. Because the image is projected by the technology called Retro-reflective Projection Technology (RPT), you can see the reflection only on the cloak and clearly even in brightness.
3.1 Retro-reflective Projection Technology(RPT) :
Now that we Ëœve seen how does optical camouflage works using RPT& Xâ„¢stal vision ,let us illustrate RPT. When using a See-Through Head-mounted Display(STHMD) to merge virtual and real environments, the operator may see the image of a virtualobject that is meant to be located behind a real object. This contradicts our intuition of depth,since the projected image of an object located behind another object in one's field of view will be obstructed at least partially. This depth cue is called occlusion, and is critical for the effectiveness of the presentation of virtual objects in three dimensions. To solve the occlusion contradiction problem, we developed RPT.
The three key techniques of RPT are the followings:
¢To use an object covered by retro-reflective material as a screen;
¢To place a projector into a position optically conjugated with the observer's eye by using
a half-mirror;
¢To make the projector's iris as small as possible (by using a pinhole).
Each of these points provides the following advantages, respectively:
Fig:5 Fig:6
Fig.5 and Fig.6 shows the principles of RPT.
The image of a virtual object is projected through a pinhole. The projected image is reflected by the half-mirror on a right angle and then retro-reflected by the retro-reflective screen.
Fig.7 optical camouflaged haptic display
Fig 7 shows the haptic display (real object) hiding the virtual object, but Optical Camouflage
Techniques permit to make the haptic display to become transparent. However the operatorâ„¢s
hand is not made transparent, which implies that it is possible to use this technology.
4.Secret of Invisibility Cloak:
If you're a fan of Harry Potter, then you're quite familiar with the concept of an invisibility cloak With optical-camouflage technology developed by scientists at the University of Tokyo, the invisibility cloak is already a reality.
This Cloaking System is designed to conceal an object from view by placing a thin video
screen between the observer and the object being concealed and at the same time presenting a
full color image of the background on the screen for view by the observer, thus creating the
illusion that the object is not there.
The special material is used as screen for RPT. Thatâ„¢s different from the screen in thecinemas. This material is called ËœRetro-reflective Materialâ„¢, and also used for the cloak. The surface of Retro-reflective Material is covered with very small beads. If the light strikes the material, the light reflects only in the same direction as it has come. So, the image is reflected clearly even in brightness.Optical camouflage requires the viewer to be in position with sensor.
The illusion is broken if you are a few meters off the mark, so this isn't exactly ready for military use. This can be used for two purposes. The first of which being showing a representation of something behind an object, on top of said object. The second is to actually change what you're looking at. This is accomplished with a reflective coating applied to the objects to receive the camouflage. Mirrors work even better. The selected background is filmed, and then projected back onto the source exactly. This is nearly unnoticeable until a highly reflective surface passes by. You then see only a little more than a shimmering outline.
In fact, we can find a lot of things using Retro-reflective Material around you. Traffic
signs, bicycleâ„¢s reflector and the lighting part of the raincoat are made from Retro reflective
Material. As like the transparent cloak, it can be seen from far away because they shine brightly by little light of the cars .
5.WHAT DO WE NEED FOR AN INVISIBILITY CLOAK
Optical camouflage doesn't work by way of magic. It works by taking advantage of something called augmented-reality technology Augmented-reality systems add computer-generated information to a user's sensory perceptions Most augmented-reality systems require that users look through a special viewing apparatus to see a real-world scene enhanced with synthesized graphics. They also require a powerful computer. Optical camouflage requires these things, as well, but it also requires several other components
Here's everything needed to make a person appear invisible:
¢ A garment made from retro-reflective material
¢ A digital video camera
¢ A computer
¢ A projector
¢ A half silvered mirror called Combiner
5.1 Garment made from a highly reflective material: The cloak that enables Optical Camouflage to work is made from a special material called retro-reflective material. A retro-reflective material is covered with thousands and thousands of small beads. When light strikes one of these beads, the light rays bounce back exactly in the same direction they came from .
In retro-reflection, the glass beads act like prisms, bending the light rays by a process known as refraction. This causes the reflected light rays to travel back along the same path as the incident light rays. The result: An observer situated at the light source receives more of the reflected light and therefore sees a brighter reflection.
Retro-reflective materials are actually quite common. Traffic signs, road markers and bicycle reflectors all take advantage of retro-reflection to be more visible to people driving at night. Movie screens used in most modern commercial theaters also take advantage of this material because it allows for high brilliance under dark conditions. In optical camouflage, the use of retro-reflective material is critical because it can be seen from far away and outside in bright sunlight.
Types of retro-reflective materials :
¢ Corner cube arrays
¢ Micro - beads
Retro-reflection in Corner Cube Arrays : Incident Light.
Retro-reflectiveGarment inMicroBeads:
Consists of thousands of micro-beads which are of 50 micro meter diameter.
¢ Micro-beads with refractive index of 2 have a retro reflective character.
¢ These micro-beads act like prisms and reflect all the rays incident on them in the same direction of the incident rays.
Types of Micro-Beads :
There are two types-
¢ Cloth type
¢ Paint type
How it all happens -Half Mirror
The role played by the Half Mirror :
¢ The projected image is reflected by a half mirror on the right angle onto the screen (the retro-reflective material) which then retro-reflects this image.
¢ The mirror has a tiny hole in it. When the user views through this hole he can see right through the retro-reflective screen
¢ Thus if properly positioned in front of the user™s eye, the half mirror allows the user to perceive both the image enhanced by the computer and the real-world scene.
2. Video Camera: The retro-reflective garment doesn't actually make a person invisible -- in fact, it's perfectly opaque. What the garment does is create an illusion of invisibility by acting like a movie screen onto which an image from the background is projected. Capturing the background image requires a video camera, which sits behind the person wearing the cloak. The video from the camera must be in a digital format so it can be sent to a computer for processing.
3. The Projector: The modified image produced by the computer must be shone onto the garment, which acts like a movie screen. A projector accomplishes this task by shining a light beam through an opening (controlled by a device called an iris diaphragm) which must be the size of a pinhole. This ensures a larger depth of field so that the screen (in this case the cloak) can be located any distance from the projector.
4. The Combiner: The system requires a special mirror to both reflect the projected image toward the cloak and to let light rays bouncing off the cloak return to the user's eye. This special mirror is called a beam splitter, or a combiner -- a half-silvered mirror that both reflects light (the silvered half) and transmits light (the transparent half). If properly positioned in front of the user's eye, the combiner allows the user to perceive both the image enhanced by the computer and light from the surrounding world. This is critical because the computer-generated image and the real-world scene must be fully integrated for the illusion of invisibility to seem realistic. The user has to look through a peephole in this mirror to see the augmented reality
More Invisibility Cloak Components:
Video Camera
¢ Capturing the background image requires a video camera, which sits behind the person wearing the cloak. The video from the camera must be in a digital format so it can be sent to a computer for processing.
Computer
¢ For optical camouflage to work, the hardware/software combo must take the captured image from the video camera, calculate the appropriate perspective to simulate reality and transform the captured image into the image that will be projected onto the retro-reflective material.
6.The Complete System:
Once a person puts on the cloak made with the retro-reflective material, here's the sequence of events:
¢ A digital video camera captures the scene behind the person wearing the cloak.
¢ The computer processes the captured image and makes the calculations necessary to adjust the still image or video so it will look realistic when it is projected.
¢ The projector receives the enhanced image from the computer and shines the image through a pinhole-sized opening onto the combiner.
¢ The silvered half of the mirror, which is completely reflective, bounces the projected image toward the person wearing the cloak.
¢ The cloak acts like a movie screen, reflecting light directly back to the source, which in this case is the mirror.
¢ Light rays bouncing off of the cloak pass through the transparent part of the mirror and fall on the user's eyes. Remember that the light rays bouncing off of the cloak contain the image of the scene that exists behind the person wearing the cloak.
¢ The person wearing the cloak appears invisible because the background scene is being displayed onto the retro-reflective material. At the same time, light rays from the rest of the world are allowed reach the user's eye, making it seem as if an invisible person exists in an otherwise normal-looking world.
7.HOW MUTUAL TELEXISTENCE WORKS:
¢ Human user A is at one location while his telexistence robot A is at another location with human user B.
¢ Human user B is at one location while his telexistence robot B is at another location with human user A.
¢ Both telexistence robots are covered in retro-reflective material so that they act like screens.
¢ With video cameras and projectors at each location, the images of the two human users are projected onto their respective robots in the remote locations.
¢ This gives each human the perception that he is working with another human instead of a robot.
¢ Right now, mutual telexistence is science fiction, but it won't be for long as scientists continue to push the boundaries of the technology.
8.APPLICATIONS:
¢Used in Stealth technology,to make airplane invisible to Radar
¢Utilization of this technology also has three important secondary energy saving byproducts:
(a) as a security instrument it can protect national strategic resources from theft and sabotage by concealing both the resource and a much reduced security force from view by either presenting the natural background on the screen or by presenting an artificial
image of the resource on the screen.
(b) its variable reflective capability could assist in heating or cooling the facility, thusrealizing considerable energy savings; and
© environmental enhancement of industrial facilities using Chameleo screens in lieu of artificial buildings/landscaping and enhancement of working spaces allowing artificialscenes on the wall and/or outside views without the need for windows.
¢Technical Advantages - The need for the camouflage aspect of this system arises out of the present state of the art of military camouflage in the visible light spectrum which isgenerally limited to techniques involving painting, coloring, and/or contour shaping to allow an object to better blend in with the background; such methods do little to conceal moving objects as their appearance must be constantly controlled from the viewpoint of the observer to blend in with the changing background.
¢Others-
1. For example, if this technique is used in cockpit for making the floor transparent at
Landing , the pilot can land safely with seeingrunway. Also, used for other vehicles like car. If you can see through the back of car, you will put the car into the garage successfully.This technique was invented from the study that skillfully mixing the real world and the world made artificially, and trying to let your life and work convenient.
2.Drivers backing up cars could benefit one day from optical camouflage. A quick glance backward through a transparent rear hatch or tailgate would make it easy to know when to stop.
9.FUTURE SCOPE:
The weak point of this technique is that the observer needs to look through a half-mirror. The current system needs a half-mirror and projectors, which were fixed on the ground.Research is currently going on to enable a person to observe the background image from various viewpoints with H.M.P. (Head-Mounted Projector)
ADVANTAGES:
¢ Optical Camouflage can be used on surgical globes or equipments so they don™t block surgeon™s view during delicate operations.
¢ In aviation, cockpit floors could become 'invisible' to assist pilots during landing.
DISADVANTAGES:
¢ The weak point of this technique is that the observer needs to look through a half-mirror. The current system needs a half-mirror and projectors, which were fixed on the ground.
Conclusion :
Creating a truly realistic optical illusion would likely require Phase Array Optics,which would project light of a specific amplitude and phase and therefore provide even greater levels of invisibility. The weak point of this technique is that the observer needs to look through a half-mirror. The current system needs a half-mirror and projectors, which were fixed on the ground. We may end up finding optical camouflage to be most useful in the environment of space, where any given background is generally less complex than earthly backdrops and therefore easier to record, process, and project.
REFERENCES
¢ http://en.wikipediawiki/Optical_camouflage
¢ http://projects.star.t.u-tokyo.ac.jp/pro...xv/oc.html
1. Introduction:
1.1 RECOGNITION OF OPTICAL CAMOUFLAGE:
In 2003, three professors at University of Tokyo †Susumu Tachi, Masahiko Inami and Naoki Kawakami †created a prototypical camouflage system in which a video camera takes a shot of the background and displays it on a cloth using an external projector. The same year Time magazine named it the coolest invention of 2003. With flexible electronics such as a flexible liquid crystal display that would permit display of the background image by the material itself, this form of optical camouflage may closely resemble its fictional counterparts.
Various methods have been proposed to integrate the visual space. In the field of Mixed Reality, one of the most popular topics is about displaying a virtual object into real world.However making objects virtually transparent, like in H.G. Wellsâ„¢ Invisible Man can also be seen as dream of human being. In this paper, we describe what could be called a camouflage technique named Optical Camouflage.
1.2 WHERE HAVE U SEEN OPTICAL CAMOUFLAGE:
¢ Ghost in the Shell.
¢ 2000 video game Deus Ex.
¢ 2002 James Bond movie Die Another Day
¢ Metal Gear Solid and Halo video game series.
¢ The video game Phantom Crash.
¢ The Predator movie.
Invisible - A Reality or fiction
Is becoming invisible confined only to the world or fiction or can it be achieved in reality The answer is YES! Thanks to the technology -Optical Camouflage with retro-reflective projection. Today invisibility is no more a fictional concept.
What makes objects visible
Before going into the concept of invisibility, let us first see what makes the objects around us visible
¢ Why are we able to see objects around us
Scattering of light
¢ A look at the law of reflection.
The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection
¢ What do we mean by Retro-reflection
Retroreflection is a special kind of reflection where the light is reflected.
Finally lets come to OPTICAL CAMOUFLAGE.
2. WHAT IS OPTICAL CAMOUFLAGE
¢ Optical camouflage is a hypothetical type of active camouflage currently only in a very primitive stage of development. The idea is relatively straightforward: to create the illusion of invisibility by covering an object with something that projects the scene directly behind that object .
¢ Optical camouflage is a kind of active camouflage which completely envelopes the wearer. It displays an image of the scene on the side opposite the viewer on it, so that the viewer can "see through" the wearer, rendering the wearer invisible.
¢ Although optical is a term that technically refers to all forms of light, most proposed forms of optical camouflage would only provide invisibility in the visible portion of the spectrum. Prototype examples and proposed designs of optical camouflage devices range back to the late eighties at least, and the concept began to appear in fiction in the late nineties.
Optical camouflage is a kind of active camouflage. This idea is very simple. If you projectbackground image onto the masked object, you can observe the masked object just as if it were virtually transparent. Although optical is a term that technically refers to all forms of light, most proposed forms of optical camouflage would only provide invisibility in the visible portion of the spectrum.
The most intriguing prototype uses an external camera placed behind the cloaked object to record a scene, which it then transmits to a computer for image processing. The computer feeds the image into an external projector which projects the image onto a person wearing a special retroreflective coat. This can lead to different results depending on the quality of the camera, the projector, and the coat, but by the late nineties, convincing illusions were created.The downside is the large amount of external hardware required, along with the fact that the illusion is only convincing when viewed from a certain angle.
Creating complete optical camouflage across the visible light spectrum would require a coating or suit covered in tiny cameras and projectors, programmed to gather visual data from a multitude of different angles and project the gathered images outwards in an equally large number of different directions to give the illusion of invisibility from all angles. For a surface subject to bending like a flexible suit, a massive amount of computing power and embedded sensors would be necessary to continuously project the correct images in all directions. This would almost certainly require sophisticated nanotechnology, as our computers, projectors, and cameras are not yet miniaturized enough to meet these conditions.
Although the suit described above would provide a convincing illusion to the naked eye of a human observer, more sophisticated machinery would be necessary to create perfect illusions in other electromagnetic bands, such as the infrared band. Sophisticated target-tracking software could ensure that the majority of computing power is focused on projecting false images in those directions where observers are most likely to be present, creating the most realistic illusionpossible.
3.HOW DOES IT WORK
Creating complete optical camouflage across the visible light spectrum would require a coating or suit covered in tiny cameras and projectors, programmed to gather visual data from a multitude of different angles and project the gathered images outwards in an equally large number of different directions to give the illusion of invisibility from all angles. For a surface subject to bending like a flexible suit, a massive amount of computing power and embedded sensors would be necessary to continuously project the correct images in all directions. This would almost certainly require sophisticated nanotechnology, as our computers, projectors, and cameras are not yet miniaturized enough to meet these conditions.
First, putting the video camera behind the person in the cloak, and capturing his background. Then, projecting the captured image onto the cloak from the projector. So, if you see from the peephole, you will see as if the cloak is transparent. Because the image is projected by the technology called Retro-reflective Projection Technology (RPT), you can see the reflection only on the cloak and clearly even in brightness.
3.1 Retro-reflective Projection Technology(RPT) :
Now that we Ëœve seen how does optical camouflage works using RPT& Xâ„¢stal vision ,let us illustrate RPT. When using a See-Through Head-mounted Display(STHMD) to merge virtual and real environments, the operator may see the image of a virtualobject that is meant to be located behind a real object. This contradicts our intuition of depth,since the projected image of an object located behind another object in one's field of view will be obstructed at least partially. This depth cue is called occlusion, and is critical for the effectiveness of the presentation of virtual objects in three dimensions. To solve the occlusion contradiction problem, we developed RPT.
The three key techniques of RPT are the followings:
¢To use an object covered by retro-reflective material as a screen;
¢To place a projector into a position optically conjugated with the observer's eye by using
a half-mirror;
¢To make the projector's iris as small as possible (by using a pinhole).
Each of these points provides the following advantages, respectively:
Fig:5 Fig:6
Fig.5 and Fig.6 shows the principles of RPT.
The image of a virtual object is projected through a pinhole. The projected image is reflected by the half-mirror on a right angle and then retro-reflected by the retro-reflective screen.
Fig.7 optical camouflaged haptic display
Fig 7 shows the haptic display (real object) hiding the virtual object, but Optical Camouflage
Techniques permit to make the haptic display to become transparent. However the operatorâ„¢s
hand is not made transparent, which implies that it is possible to use this technology.
4.Secret of Invisibility Cloak:
If you're a fan of Harry Potter, then you're quite familiar with the concept of an invisibility cloak With optical-camouflage technology developed by scientists at the University of Tokyo, the invisibility cloak is already a reality.
This Cloaking System is designed to conceal an object from view by placing a thin video
screen between the observer and the object being concealed and at the same time presenting a
full color image of the background on the screen for view by the observer, thus creating the
illusion that the object is not there.
The special material is used as screen for RPT. Thatâ„¢s different from the screen in thecinemas. This material is called ËœRetro-reflective Materialâ„¢, and also used for the cloak. The surface of Retro-reflective Material is covered with very small beads. If the light strikes the material, the light reflects only in the same direction as it has come. So, the image is reflected clearly even in brightness.Optical camouflage requires the viewer to be in position with sensor.
The illusion is broken if you are a few meters off the mark, so this isn't exactly ready for military use. This can be used for two purposes. The first of which being showing a representation of something behind an object, on top of said object. The second is to actually change what you're looking at. This is accomplished with a reflective coating applied to the objects to receive the camouflage. Mirrors work even better. The selected background is filmed, and then projected back onto the source exactly. This is nearly unnoticeable until a highly reflective surface passes by. You then see only a little more than a shimmering outline.
In fact, we can find a lot of things using Retro-reflective Material around you. Traffic
signs, bicycleâ„¢s reflector and the lighting part of the raincoat are made from Retro reflective
Material. As like the transparent cloak, it can be seen from far away because they shine brightly by little light of the cars .
5.WHAT DO WE NEED FOR AN INVISIBILITY CLOAK
Optical camouflage doesn't work by way of magic. It works by taking advantage of something called augmented-reality technology Augmented-reality systems add computer-generated information to a user's sensory perceptions Most augmented-reality systems require that users look through a special viewing apparatus to see a real-world scene enhanced with synthesized graphics. They also require a powerful computer. Optical camouflage requires these things, as well, but it also requires several other components
Here's everything needed to make a person appear invisible:
¢ A garment made from retro-reflective material
¢ A digital video camera
¢ A computer
¢ A projector
¢ A half silvered mirror called Combiner
5.1 Garment made from a highly reflective material: The cloak that enables Optical Camouflage to work is made from a special material called retro-reflective material. A retro-reflective material is covered with thousands and thousands of small beads. When light strikes one of these beads, the light rays bounce back exactly in the same direction they came from .
In retro-reflection, the glass beads act like prisms, bending the light rays by a process known as refraction. This causes the reflected light rays to travel back along the same path as the incident light rays. The result: An observer situated at the light source receives more of the reflected light and therefore sees a brighter reflection.
Retro-reflective materials are actually quite common. Traffic signs, road markers and bicycle reflectors all take advantage of retro-reflection to be more visible to people driving at night. Movie screens used in most modern commercial theaters also take advantage of this material because it allows for high brilliance under dark conditions. In optical camouflage, the use of retro-reflective material is critical because it can be seen from far away and outside in bright sunlight.
Types of retro-reflective materials :
¢ Corner cube arrays
¢ Micro - beads
Retro-reflection in Corner Cube Arrays : Incident Light.
Retro-reflectiveGarment inMicroBeads:
Consists of thousands of micro-beads which are of 50 micro meter diameter.
¢ Micro-beads with refractive index of 2 have a retro reflective character.
¢ These micro-beads act like prisms and reflect all the rays incident on them in the same direction of the incident rays.
Types of Micro-Beads :
There are two types-
¢ Cloth type
¢ Paint type
How it all happens -Half Mirror
The role played by the Half Mirror :
¢ The projected image is reflected by a half mirror on the right angle onto the screen (the retro-reflective material) which then retro-reflects this image.
¢ The mirror has a tiny hole in it. When the user views through this hole he can see right through the retro-reflective screen
¢ Thus if properly positioned in front of the user™s eye, the half mirror allows the user to perceive both the image enhanced by the computer and the real-world scene.
2. Video Camera: The retro-reflective garment doesn't actually make a person invisible -- in fact, it's perfectly opaque. What the garment does is create an illusion of invisibility by acting like a movie screen onto which an image from the background is projected. Capturing the background image requires a video camera, which sits behind the person wearing the cloak. The video from the camera must be in a digital format so it can be sent to a computer for processing.
3. The Projector: The modified image produced by the computer must be shone onto the garment, which acts like a movie screen. A projector accomplishes this task by shining a light beam through an opening (controlled by a device called an iris diaphragm) which must be the size of a pinhole. This ensures a larger depth of field so that the screen (in this case the cloak) can be located any distance from the projector.
4. The Combiner: The system requires a special mirror to both reflect the projected image toward the cloak and to let light rays bouncing off the cloak return to the user's eye. This special mirror is called a beam splitter, or a combiner -- a half-silvered mirror that both reflects light (the silvered half) and transmits light (the transparent half). If properly positioned in front of the user's eye, the combiner allows the user to perceive both the image enhanced by the computer and light from the surrounding world. This is critical because the computer-generated image and the real-world scene must be fully integrated for the illusion of invisibility to seem realistic. The user has to look through a peephole in this mirror to see the augmented reality
More Invisibility Cloak Components:
Video Camera
¢ Capturing the background image requires a video camera, which sits behind the person wearing the cloak. The video from the camera must be in a digital format so it can be sent to a computer for processing.
Computer
¢ For optical camouflage to work, the hardware/software combo must take the captured image from the video camera, calculate the appropriate perspective to simulate reality and transform the captured image into the image that will be projected onto the retro-reflective material.
6.The Complete System:
Once a person puts on the cloak made with the retro-reflective material, here's the sequence of events:
¢ A digital video camera captures the scene behind the person wearing the cloak.
¢ The computer processes the captured image and makes the calculations necessary to adjust the still image or video so it will look realistic when it is projected.
¢ The projector receives the enhanced image from the computer and shines the image through a pinhole-sized opening onto the combiner.
¢ The silvered half of the mirror, which is completely reflective, bounces the projected image toward the person wearing the cloak.
¢ The cloak acts like a movie screen, reflecting light directly back to the source, which in this case is the mirror.
¢ Light rays bouncing off of the cloak pass through the transparent part of the mirror and fall on the user's eyes. Remember that the light rays bouncing off of the cloak contain the image of the scene that exists behind the person wearing the cloak.
¢ The person wearing the cloak appears invisible because the background scene is being displayed onto the retro-reflective material. At the same time, light rays from the rest of the world are allowed reach the user's eye, making it seem as if an invisible person exists in an otherwise normal-looking world.
7.HOW MUTUAL TELEXISTENCE WORKS:
¢ Human user A is at one location while his telexistence robot A is at another location with human user B.
¢ Human user B is at one location while his telexistence robot B is at another location with human user A.
¢ Both telexistence robots are covered in retro-reflective material so that they act like screens.
¢ With video cameras and projectors at each location, the images of the two human users are projected onto their respective robots in the remote locations.
¢ This gives each human the perception that he is working with another human instead of a robot.
¢ Right now, mutual telexistence is science fiction, but it won't be for long as scientists continue to push the boundaries of the technology.
8.APPLICATIONS:
¢Used in Stealth technology,to make airplane invisible to Radar
¢Utilization of this technology also has three important secondary energy saving byproducts:
(a) as a security instrument it can protect national strategic resources from theft and sabotage by concealing both the resource and a much reduced security force from view by either presenting the natural background on the screen or by presenting an artificial
image of the resource on the screen.
(b) its variable reflective capability could assist in heating or cooling the facility, thusrealizing considerable energy savings; and
© environmental enhancement of industrial facilities using Chameleo screens in lieu of artificial buildings/landscaping and enhancement of working spaces allowing artificialscenes on the wall and/or outside views without the need for windows.
¢Technical Advantages - The need for the camouflage aspect of this system arises out of the present state of the art of military camouflage in the visible light spectrum which isgenerally limited to techniques involving painting, coloring, and/or contour shaping to allow an object to better blend in with the background; such methods do little to conceal moving objects as their appearance must be constantly controlled from the viewpoint of the observer to blend in with the changing background.
¢Others-
1. For example, if this technique is used in cockpit for making the floor transparent at
Landing , the pilot can land safely with seeingrunway. Also, used for other vehicles like car. If you can see through the back of car, you will put the car into the garage successfully.This technique was invented from the study that skillfully mixing the real world and the world made artificially, and trying to let your life and work convenient.
2.Drivers backing up cars could benefit one day from optical camouflage. A quick glance backward through a transparent rear hatch or tailgate would make it easy to know when to stop.
9.FUTURE SCOPE:
The weak point of this technique is that the observer needs to look through a half-mirror. The current system needs a half-mirror and projectors, which were fixed on the ground.Research is currently going on to enable a person to observe the background image from various viewpoints with H.M.P. (Head-Mounted Projector)
ADVANTAGES:
¢ Optical Camouflage can be used on surgical globes or equipments so they don™t block surgeon™s view during delicate operations.
¢ In aviation, cockpit floors could become 'invisible' to assist pilots during landing.
DISADVANTAGES:
¢ The weak point of this technique is that the observer needs to look through a half-mirror. The current system needs a half-mirror and projectors, which were fixed on the ground.
Conclusion :
Creating a truly realistic optical illusion would likely require Phase Array Optics,which would project light of a specific amplitude and phase and therefore provide even greater levels of invisibility. The weak point of this technique is that the observer needs to look through a half-mirror. The current system needs a half-mirror and projectors, which were fixed on the ground. We may end up finding optical camouflage to be most useful in the environment of space, where any given background is generally less complex than earthly backdrops and therefore easier to record, process, and project.
REFERENCES
¢ http://en.wikipediawiki/Optical_camouflage
¢ http://projects.star.t.u-tokyo.ac.jp/pro...xv/oc.html
